It has generally been considered that meiotic prophase develops directly from interphase, and cytochemical and radiation experiments are conducted on this basis. However it is now established in many materials that a mitosis-like phase of chromosome contraction occurs just prior to leptotene; these contracted chromosomes then despiralize to leptotene. The degree of chromosome contraction can be extremely variable. This "preleptotene chromosome contraction" was described by the applicant in one cultivar of Lilium and it was shown for the first time that degree of contraction may be related to sequence of development of the meiocytes. The same kind of preleptotene contraction has been observed in numerous animals, and it was recently found in human meiosis. Three cultivars of Lilium have now been compared and the following data obtained: (1) There is a genetic basis for differences in preleptotene contraction among different cultivars; (2) The degree of chromosome contraction may be related to sequence of development of buds on the plant, and perhaps in this way to age of individual; (3) Within each reproductive organ the first developing meiocytes exhibit a greater degree of preleptotene contraction than later developing meiocytes. On the basis of these observations it is proposed that one of the initial events of meiosis is the inhibition of mitotic coiling. If mitotic coiling inhibition is delayed, preleptotene contraction results, and the longer the delay the more extreme the contraction. The present objectives are: (1) Determination of the relationship between degree of preleptotene contraction and age of the individual; (2) Determination of the relationship between preleptotene contraction and chiasma frequency; (3) Additional information concerning genetic background on expression of the contraction state. Lilium is the only material in which the limits of variability of preleptotene contraction have been determined and consequently the best suited material for such studies.